1. Field of the Invention
The present invention relates to a compact disc reproduction apparatus, and more particularly to a sub-que code (Q subcode) data read circuit for a compact disc reproduction apparatus constructed to convert sub-que code data of serial bits output from the CD-DSP of a CD-ROM drive into that of parallel bytes and to adjust positions of bits in the parallel bytes so that a microcomputer can read the sub-que code data through the sub-que code data read circuit without directly reading the data, thereby capable of reproducing data recorded on a compact disc at a high speed.
2. Description of the Prior Art
Generally, sub-que code data, which is obtained when data recorded on a compact disc is reproduced in a compact disc reproduction apparatus, contains information relating to the data being reproduced. The information contained in such sub-que code data includes data position (time) information, music information, data characteristic and etc.. Such sub-que code data is constituted by 10 bytes (namely, 80 bits) per block (1/75 second at a single reproducing speed).
When data recorded on a compact disc is reproduced using a CD-ROM drive, sub-que code data is usually detected.
Referring to FIG. 1, there is illustrated a CD-ROM drive as a conventional compact disc reproduction apparatus. As shown in FIG. 1, the CD-ROM drive includes a pick-up 10 for convening data recorded on a disc into an electrical signal, a radio frequency amplifier 20 for amplifying the electrical signal output from the pick-up 10, and a compact disc-digital signal processor (CD-DSP) 30 for processing an output from the radio frequency amplifier 20 in a digital manner, thereby reproducing general data and sub-que code data. The CD-ROM drive also includes a microcomputer 40 for reading the sub-que code data output from the CD-DSP 30 and thereby discriminating data recorded on the compact disc, a CD-ROM DSP 50 for processing the general data output from the CD-DSP 30 in a digital manner, a RAM 60 for storing the general data output from the CD-ROM DSP 50, and an interface 70 for coupling both the microcomputer 40 and the CD-ROM DSP 50 to a personal computer PC.
Now, the sub-que code data reading operation of the compact disc reproduction apparatus having the above-mentioned construction will be described in conjunction with FIGS. 1 to 3.
Once the pick-up 10 converts data recorded on a compact disc into an electrical signal, it sends the signal to the radio frequency amplifier 20 which, in turn, amplifies the received signal to a desired level. The amplified signal is then applied to the CD-DSP 30.
The CD-DSP 30 processes the output from the radio frequency amplifier 20 in a digital manner, thereby reproducing general data and sub-que code data including data position (time) information, music information, data characteristic, etc., all relating to the data recorded on the compact disc. The CD-ROM DSP 50 receives the general data from the CD-DSP 30 and processes it in a digital manner. The CD-ROM DSP 50 then stores the processed data in the RAM 60. Meanwhile, the microcomputer 40 reads the sub-que code data from the CD-DSP 30 and discriminates information about the data recorded on the compact disc on the basis of the sub-que code data. This will be described in more detail.
Every time the CD-DSP 30 detects sub-que code data of one block (10 bytes) as it processes the output from the radio frequency amplifier 20 in a digital manner, it outputs a synchronous signal SCOR with a high level as shown in FIG. 2A. Thereafter, the CD-DSP 30 sends an error checking signal CRCF (FIG. 2C) to the microcomputer 40. The error checking signal CRCF is indicative of whether a group of sub-que code data in the current block has an error.
Upon receiving the synchronous signal SCOR and the error checking signal CRCF, the microcomputer 40 checks whether the sub-que code data group of the current block has an error, based on the error checking signal CRCF. When the error checking signal CRCF has a level of "1", that is, when no error is involved, the microcomputer 40 outputs a clock signal SQCK with a level of "0" as shown in FIG. 2B. Thereafter, the microcomputer 40 outputs a clock signal SQCK with a level of "1" to read and store the first one-bit Q5 of the sub-que code data SUBQ as shown in FIG. 2C. After completing the reading and storing operation for the first one-bit Q5, the microcomputer 40 outputs a clock signal SQCK with a level of "0" and then with a level of "1" to read and store the second one-bit Q6 of the sub-que code data SUBQ. The microcomputer 40 then repeats the above procedure until the 8th one-bit Q4 is read and stored. Thereafter, the microcomputer 40 converts the sub-que code data read and stored one bit by one bit into that of one byte. After completing the conversion, bits of the first one-byte data are adjusted in position to have the order of Q8, Q7, Q6, Q5, Q4, Q3, Q2 and Q1. The rearranged first one-byte data is then stored.
Subsequently, the microcomputer 40 reads the next bit string of the sub-que code data SUBQ by bits and converts it into that of one byte. This second one-byte sub-que code data is then stored. The microcomputer 40 then repeats this procedure until the 10th one-byte sub-que code data is stored, thereby completing reading for the sub-que code data of one block. After completing this reading, the microcomputer 40 completes the overall reading procedure.
In other words, the microcomputer 40 reads 80 bits of the sub-que code data in a sequential manner as it generates 80 clock signals SQCK sequentially. After reading the data, the microcomputer 40 converts the data read by bits into that of bytes. For each byte, its bits are adjusted in position to have a desired bit order. As this adjustment operation is executed 10 times, the reading operation for the sub-que code data of one block (10 bytes=80 bits) is completed. After completing this reading operation, the data recorded on the compact disc, which includes data position (time) information, music information, data characteristic etc., are discriminated through an operating procedure.
Thereafter, the CD-ROM drive, which is an example of a compact disc reproduction apparatus, sends general data and sub-que code data stored in the RAM 60 to the personal computer PC via the interface 70 so that the data recorded on the compact disc can be reproduced. As mentioned above, the sub-que code data includes data position (time) information, music information, data characteristic, etc.
In the conventional compact disc reproduction apparatus wherein the microcomputer 40 directly reads the sub-que code data from the CD-DSP 30, the microcomputer 40 should execute, for every interval of clock pulses, executive codes involving at least four processing steps, that is, a bit clearing operation (BIT CLEAR) for clearing the bit as "0", a bit setting operation (BIT SET) for setting the bit as "1", a move operation (MOVE) for reading the serial sub-que code data, and a shift operation (SHIFT) for storing the read data. As a result, the microcomputer 40 should execute executive codes involving at least 34 processing steps in the case of reading one byte and involving at least 340 processing steps in the case of reading one block.
Where the microcomputer 40 is of the medium grade having an internal frequency of 5 MHz, a time of about 2 to 3 .mu.sec is taken in executing each of the commands such as BIT CLEAR, BIT SET, MOVE or SHIFT. Accordingly, a time of about 0.7 to 1.2 msec is taken in the case wherein executive codes involving 340 processing steps are executed to read sub-que code data of one block.
However, the microcomputer used in the compact disc reproduction apparatus must not consume too much time in reading the sub-que code data because it also has to execute a transfer of the read sub-que code data to a personal computer and control internal servo circuits in addition to the reading operation for the sub-que code data.
Where sub-que code data of one block is reproduced at a single speed (1/75 sec=13.3 msec), the above-mentioned time of about 0.7 to 1.2 msec causes no problem in the conventional compact disc reproduction apparatus. However, such time becomes problematic at double, triple or quadruple reproduction speed.
At quadruple reproduction speed, for example, the data reading time of about 0.7 to 1.2 msec becomes obstructive to the real-time reproduction of the CD-ROM drive because about 1/3 of the entire reproduction time (3.3 msec) is consumed to read the sub-que code data.
In order to reduce the load of the microcomputer in the CD-ROM drive, a scheme has also been made wherein another microcomputer is added to distribute the total microcomputer's load. However, this scheme has problems of an increase in cost and problems of requiring a complex interface between the microcomputers.